The present invention relates to niobium powders and electrolytic capacitors using the niobium powders as well as methods of making the powders and electrolytic capacitors.
For many years, it has been the coal of various researchers to develop niobium electrolytic capacitors because of the high di-electric constant of its oxide and the relativly low cost of niobium compared to a variety of other metals. Initially, researchers in this field considered the possibility of using niobium as a substitute for tantalum capacitors. Accordingly, many studies were conducted to determine the suitability of replacing tantalum with niobium.
In some of these studies, however, it was concluded that niobium has serious fundamental deficiencies that needed to be resolved, thus inferring that niobium was not an acceptable substitute for tantalum. (See J. Electrochem. Soc. p. 408 C, Dec. 1977). In another study, one conclusion reached was that the use of niobium in solid electrolytic capacitors seems very unlikely due to various physical and mechanical problems, such as field crystallization. (Electrocomponent Science and Technology, Vol. 1, pp. 27-37 (1974)). Further, in another study, the researchers concluded that anodically formed passive films on niobium were different from electrical properties accomplished with tantalum and that the use of niobium led to complexities which were not present with tantalum. (See Elecrochimica Act., Vol. 40, no. 16, pp. 2623-26 (1995)). Thus, while there was initial hope that niobium might be a suitable replacement for tantalum, the evidence showed that niobium was not capable of replacing tantalum in the electrolytic capacitor market.
Besides tantalum electrolytic capacitors, there is a market for aluminum electrolytic capacitors. However, the aluminum electrolytic capacitors have dramatically different performance characteristics from tantalum electrolytic capacitors.
A driving force in electronic circuitry today is the increasing move toward lower Equivalent Series Resistance (ESR) and Equivalent Series Inductance (ESL). As IC performance increases with submicron geometry, there is a need for lower power supply voltage and noise margin. At the same time, increasing IC speeds require higher power needs. These conflicting requirements create a demand for better power management. This is being accomplished through distributed power supplies which need larger currents for decoupling noise. Increasing IC speeds also mean lower switching times and higher current transients. The electrical circuit must, therefore, also be designed to reduce the transient load response. This broad range of requirements can be met if the circuit has large enough capacitance but low ESR and ESL.
Aluminum capacitors typically provide the largest capacitance of all capacitor types. ESR decreases with increase in capacitance. Therefore, currently a large bank of high capacitance aluminum capacitors are used to meet the above requirements. However, aluminum capacitors do not really satisfy the designers"" requirements of low ESR and ESL. Their mechanical construction with liquid electrolyte inherently produce ESR in the 100s of milliohm along with high impedance.
A feature of the present invention is to provide flaked niobium powders.
A further feature of the present invention is to provide niobium powders, preferably having high surface areas and physical characteristics which permit the niobium powders to be formed into a capacitor having high capacitance.
Another feature of the present invention is to provide niobium powders which, when formed into capacitors, have a low DC leakage.
An additional feature of the present invention is to provide a method of reducing the DC leakage in a capacitor formed from niobium powder.
Additional features and advantages of the present invention will be set forth in part in the description which follows, and in part will be apparent from the description, or may be learned by practice of the present invention.
The present invention relates to a flaked niobium powder. Another aspect of the present invention relates to any niobium powder having a BET surface area of at least about 0.15 m2/g.
The present invention also relates to a niobium powder, which when formed into an electrolytic capacitor anode, the anode has a capacitance of 30,000 CV/g to about 61,000 CV/g.
The present invention, in addition, relates to a niobium powder having an oxygen content W of at least about 2,000 ppm.
Also, the present invention relates to a method to reduce DC leakage in a niobium anode made from niobium powder which comprises the step of doping the niobium powder with a sufficient amount of oxygen to reduce the DC leakage.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the present invention, as claimed.